Babyen blir vanligvis stille når hun får smokken sin og en varm tåteflaske.

Because babyen is the definite form: the baby.

In Norwegian, you usually mark definiteness by adding an ending to the noun:

• en baby = a baby
• babyen = the baby

So Norwegian often does with an ending what English does with the separate word the.

Blir is the present tense of bli, which often means become or get.

So:

• Babyen er stille = the baby is quiet
• Babyen blir stille = the baby becomes / gets quiet

In this sentence, the idea is that the baby changes state after getting the pacifier and bottle. That is why blir is more natural than er.

This is normal Norwegian word order in a main clause.

Norwegian is usually a verb-second language in main clauses. That means the finite verb tends to come in the second position:

• Babyen = first element
• blir = second element
• vanligvis comes after that

So Babyen blir vanligvis stille ... is the expected pattern.

You could also say:

• Vanligvis blir babyen stille ...

That just puts more focus on usually.

Because når introduces a subordinate clause, and subordinate clauses do not use the normal main-clause verb-second pattern.

So after når, the subject usually comes before the verb:

• når hun får ... = when she gets ...

Compare:

• Main clause: Hun får smokken sin.
• Subordinate clause: ... når hun får smokken sin.

So når får hun would sound like a direct question: when does she get ...?

Here it is basically when, but in a habitual sentence like this it can feel a lot like whenever.

Because of vanligvis (usually), the sentence describes a repeated pattern, not one single event. So the sense is:

• when / whenever she gets her pacifier and a warm baby bottle

Both ideas fit the context, even though Norwegian just uses når.

Here får means something like gets, receives, or is given.

So hun får smokken sin og en varm tåteflaske means that she is given, or receives, those things.

This is a very common Norwegian verb, and it can cover several English ideas depending on context:

• få en gave = get a gift
• få hjelp = get help
• få mat = get food

Because the sentence describes a general habit or usual situation.

Just like English says:

• The baby usually gets quiet when she gets her pacifier...

Norwegian uses the present tense for this kind of repeated, general truth:

• Babyen blir vanligvis stille når hun får ...

So it is not talking about only one specific moment.

Because sin is the reflexive possessive. It is used when the owner is the same as the subject of the clause.

In the clause:

• når hun får smokken sin

the subject is hun, and the pacifier belongs to her, so Norwegian normally uses sin.

This is a very important pattern:

• Hun tar boka si. = She takes her own book.
• Hun tar boka hennes. = She takes her book, but now her usually means some other female person's book.

So smokken sin means the pacifier belonging to the baby herself.

Because these forms agree with the thing being owned, not with the owner.

Here the possessed noun is smokken, which is singular and common gender, so the correct form is sin.

The basic pattern is:

• sin = common gender singular
• si = feminine singular
• sitt = neuter singular
• sine = plural

So:

• smokken sin = her pacifier
• barnet sitt = her child
• skoene sine = her shoes

Because tåteflaske is a singular common-gender noun, and after en, the adjective usually takes its basic form.

So:

• en varm tåteflaske = correct

Compare:

• en varm flaske = common gender singular
• et varmt måltid = neuter singular
• varme flasker = plural
• den varme flasken = definite

So varm is correct here because tåteflaske is singular and common gender.

Because Norwegian normally writes compound nouns as a single word.

So tåteflaske is one compound noun:

• tåte
  • flaske

This is extremely common in Norwegian. For example:

• barnevogn = baby stroller
• sykehus = hospital
• fotballspiller = football player

English often writes these as two words or with different spelling habits, but Norwegian strongly prefers one-word compounds.

Yes. If the baby is female, hun is completely natural.

So this sentence implies that the baby is a girl, or that the speaker is referring to the baby as female.

If the sex is unknown or irrelevant, Norwegian often repeats the noun instead of using a neutral personal pronoun:

• Babyen blir stille når babyen får ...

Using den for a baby would usually sound impersonal, because den/det are normally not used for people.

Here stille is an adjective, and it is being used predicatively after blir.

So:

• babyen blir stille = the baby gets quiet

This is the same kind of structure as:

• Han blir trøtt = he gets tired
• Vannet blir kaldt = the water gets cold

With stille, the form stays stille here. It is simply the normal adjective form in this expression.